According to FBI files, Carter was reported to "actively uphold Russia's policies"[8] and displayed "every indication that he has been closely associated with leading members of the Communist Party in the United States."[9] For example, in 1938, Carter recommended Communist Party Secretary Earl Browder to a Canadian club as a possible speaker, saying that Browder, "contrary to the public view, is 100% American."[10]

In a 1938 letter, IPR Trustee Owen Lattimore congratulated Carter: "I think that you are pretty cagey in turning over so much of the China section of the inquiry to Asiaticus, Han-seng and Chi. They will bring out the absolutely essential radical aspects, but can be depended on to do it with the right touch..."[11] “Asiaticus” was the Polish-born Comintern agent Moses Wolf Grzyb, alias M. G. Shippe (or Schiffe), alias Hans (or Heinz) Muëller (or Moëller);[12] “Han-seng” refers to refers to Chen Han-seng, a Comintern recruit and "a member of the well-known Richard Sorge Spy Ring";[13][14][15][16] “Chi” was Red Chinese secret agent Chi Chao-ting (Ji Chaoding).[17]

Also in 1938, when many other formerly loyal friends of the Soviet Union were becoming disillusioned by Stalin’s Great Purge,[18] Carter defended the show trials, saying the Russian people “are thankful that their government has at last been firm in dealing with what they regard as Fascist-supported intrigue to overthrow the Government of the Soviet Union.” This apologia was reprinted in full in Soviet Russia Today, which identified Carter as a frequent contributor to “our leading periodicals.”[19]

Carter endorsed the Hitler-Stalin pact, according to the socialist magazine New Leader,[20] but after the German invasion of the Soviet Union, he "proposed a toast to the success of the Soviet resistance to the Nazis and referred to Russia as the 'beloved Motherland of so many of us here tonight'"[21] and made a speech describing "the fight being waged by the Russian people in the defense of the democracies."[22]

Louis Budenz, former managing editor of the Daily Worker, told FBI investigators "that he had numerous dealings with Carter, while on the 'Daily Worker' staff, and that these dealings 'were on a plane based on the fact that he was a member of the Communist Party.'"[23] On April 22, 1948, Budenz advised, "Edward C. Carter was certainly under Communist Party discipline. I recall Jack Stachel, member of the national board of the Communist Party, stating that "Because the Russian War Relief Program is not going right, we will have to order Carter to realize his responsibility and continue his job. He is not running a community fund; he will have to live up to his Party responsibility."[24]

One teletype in the FBI's IPR file cites a source (redacted) to the effect that there was, since 1936, "a concerted effort to install men who had been screened by [Frederick Vanderbilt] Field or Carter or other members of the IPR into the State Dept.”[25]

Another memo in the file, by an IPR regional officer, alleges that Carter "may have been connected with the Communists in some way.... his political views are way to the left.... I have little confidence in his basic honesty."[26]